How to Build a Homemade Theremin Using Basic Electronic Components

Introduction

A theremin is an electronic musical instrument that is played without physical contact. Instead, the musician controls pitch and volume by moving their hands in proximity to two antennae. Theremins produce an eerie, wavering sound that has been used in many 1950s science fiction films.

Building your own theremin at home can be a fun electronics project that allows you to explore radio frequencies and analog circuitry. With just a few basic components, I was able to assemble a simple, functional theremin using tutorials I found online. In this article, I will walk through the step-by-step process I used to build a homemade theremin using basic electronic parts.

Gather the Required Components

The simplest theremin circuits can be built using just a handful of parts:

• Two antennae - These can be made from metal rods, stiff wire, or even coat hangers. One antenna controls pitch and the other controls volume.

• One oscillator - This circuit produces the tone that is controlled by the pitch antenna. Common oscillators used include 555 timer chips or Colpitts oscillators.

• One amplifier - An audio amplifier boosts the oscillator's signal so it can be heard. LM386 audio amplifier chips work well.

• Resistors and capacitors - These additional passive components help shape the oscillator's tone and modulate the audio signal.

• Speaker - Any 8-ohm speaker will work to convert the electrical signal into audible sound.

• 9V battery and clip - Battery powers the theremin's circuitry. 9V works well for 555 timer osciallators.

For a simple theremin, this is all you need! Additionally, a solder-able breadboard and various wires are necessary to connect it all together.

Construct the Pitch Control Circuitry

The pitch antenna needs circuitry that converts the hand movements into electrical signals that control the oscillator's pitch. Here are the steps I took:

• Connect the pitch antenna to a resistor and capacitor. This forms a simple RC circuit that filters radio frequencies picked up by the antenna.

• Connect the capacitor to the oscillator's voltage control input. As your hand gets closer to the antenna, the capacitance increases, changing the voltage on the oscillator and raising the pitch.

• Start with a 1Mohm resistor and 220pF capacitor. Adjust these values to calibrate the oscillator's pitch range.

• Use shielded wire for the antenna. This reduces interference. An extending metal antenna works best.

The pitch circuitry has to be tuned carefully to sweep through the full melodic range you want. Trying different resistor and capacitor values helps dial in the proper range.

Construct the Volume Control Circuitry

The volume antenna needs circuitry that converts hand movements into electrical signals that control the amplifier's gain. Here is how I built mine:

• Connect the volume antenna to a resistor and capacitor, forming another RC filter.

• Connect the capacitor to the amplifier's gain control. As your hand gets closer, the amplifier's gain increases, making the theremin louder.

• Use a 1Mohm resistor and 1nF capacitor to start. Adjust as needed to control the volume range.

• Use shielded wire for the antenna. Unshielded wire is prone to hum and interference.

The volume circuit should allow the theremin to be turned down completely when your hand is farthest from the antenna. Move your hand closer until the maximum volume is reached.

Combine the Oscillator and Amplifier Circuits

The last step is to connect the pitch control circuitry to the oscillator and connect the oscillator's output to the audio amplifier:

• Connect the oscillator output to the amplifier's input. This sends the tone to the amplifier.

• Connect power and ground wires. Use the 9V battery pack to power both the oscillator and amplifier.

• Connect the speaker to the amplifier output. The speaker converts the electrical signal into audible sound waves.

• Optionally, add a power switch and status LEDs. This allows the circuit to be powered on and off and adds LED indicators.

Once everything is connected, you should have a working theremin! Adjusting the component values and antenna positions can fine tune the pitch range and volume response.

Refinements for Better Performance

Here are some additional steps you can take to improve your homemade theremin:

• Add capacitors across power connections to smooth out voltage fluctuations.

• Use shielded enclosures for the oscillator and amp to reduce interference.

• Experiment with different antenna shapes and positions to fine tune pitch and volume response.

• Add a loop antenna to control loudness of higher frequencies separately.

• Build a sturdier case with a stand for the antenna and nice knobs or dials.

• Add a tremolo circuit to create a wavering vibrato effect in the tone.

With some tweaking and refinement, you can build a nice sounding theremin using basic components and a bit of electronics knowledge. Just take it step-by-step. Soon you'll be making eerie sci-fi music!